I've been bothered by sciatica for about the last 3 years. In that time I've tried to learn alot about it and even wrote a 10 page paper on it.
Your best bet is to do a simple Yahoo search to get info but I'll tell you what I remember.
It can be caused by tightness in anyone of the little muscles in you ass. Most commonly it is because of a herniated disc (either bulging or ruptured in nature).
I was seeing a chiropractor for quite a while and that made the pain go away.... but it would allways come back. I am now seeing an athletic therapist in conjuction with a non-traditional chiropractor (non of that hard cracking stuff) I'm receiving acupuncture, laser therapy and active release. At the same time I am doing plenty of mckenzie back extensions (lie flat on the floor and do a "push-up" but keep your legs/hips on the floor) I am also receiving plenty of active release treatment. I also been spending time off the roads and in the pool running. I am currently getting much better.
I really recommend that you either see a chiropractor that is trained in athletic therapy/active release, or better yet, go to a multi-disciplinary clinc where you can receive attention to the muscles as well as to the joint. Most injuries involve bth, so both must be treated.
I also take Advil occasionally to numb the pain so i can sleep.
It can also help to strenghtn your postural muscles (lower back and abdominals)
And don't sit on your wallet.
Let me know if you have any other questions.
and don't slouch.